<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
  </head>

  <body>
    <input type="text" /> <button>点击</button>
    <div></div>
    <script>
      // trim 方法去除字符串两侧空格
      var str = "   mo  on   "
      console.log(str)
      var str1 = str.trim()
      console.log(str1)
      var input = document.querySelector("input")
      var btn = document.querySelector("button")
      var div = document.querySelector("div")
      btn.onclick = function () {
        var str = input.value.trim()
        if (str === "") {
          alert("请输入内容")
        } else {
          console.log(str)
          console.log(str.length)
          div.innerHTML = str
        }
      }
    </script>
  </body>
</html>
